Fourty six isolates of K. pneumoniae were studied. The strains were cultured from different clinical specimens received from children hospitalized at University Hospital in Bydgoszcz. One strain was cultured from hospital environment. Production of ESBL was assessed using double disk synergy test and confirmatory test. The genomic DNA was extracted from the strains separated by PFGE after digesting with XbaI endonuclease. Production of ESBL was detected in 73.9% of K. pneumoniae isolates. Molecular typing results revealed a great genetic diversity among K. pneumoniae isolates. All repeated PFGE patterns were detected only in four K. pneumoniae isolates.